In Jesus’ time, there was a tax collected (tribute) for the Roman emperor, in addition to the numerous local Judaean taxes. During one of these collections, Jesus said: “Shew me the tribute money. And they brought unto him a penny (King James translation for a silver denarius). And he saith unto them, Whose is this image and superscription? They say unto him, Caesar’s. Then saith he unto them, Render therefore unto Caesar the things which are Caesar’s, and unto God the things that are God’s (Matthew 22:19-21). The coin referred to is generally considered to be a silver Roman denarius featuring the likeness of the Emperor Tiberius (14-37 CE) on one side, and his mother Livia, seated on a throne, on the reverse.
“The Tribute Penny” - Silver Denarius issued by Emperor Tiberius (14-37 CE). (NFA XVIII, lot 426)
Sources: The Handbook of Biblical Numismatics